2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 162

Ignition Positions The ignition switch has four different positions. A (LOCK/OFF): This position locks the ignition. It also locks the transmission on automatic transmission vehicles. The key can be removed in LOCK/OFF. On vehicles with an automatic transmission, the shift lever must be in P (Park) to turn the ignition switch to LOCK/OFF. The steering can bind with the wheels turned off center. If this happens, move the steering wheel from right to left while turning the key to ACC/ACCESSORY. If this doesn't work, then the vehicle needs service. Notice: Using a tool to force the key to turn in the ignition could cause damage to the switch or break the key. Use the correct key, make sure it is all the way in, and turn it only with your hand. If the key cannot be turned by hand, see your dealer. To shift out of P (Park), the ignition must be in ON/RUN or ACC/ACCESSORY and the regular brake pedal must be applied. 3-24